Dual channel telegraph system



zsheets-sheet 1 Filed July 5, 1948 A 7' TURA/EV Aug. 25,1953 s. D. BRowNlNG DUAL CHANNEL TELEGRAPH SYSTEM 2 Sheets-Sheet 2 Filed July 3, 1948` INVENTOR.` sAMz/fl. 0. @RaW/ww ATTORNEY mw, ---n N5 l a., l??? a@ w, 11.52.; Nw\

. IIIIA IIIL Patented Aug. 25, 1953 Samuel D. Browning, Mackay Radio and Baldwin, N. Y., assignor to Telegraph Company, New

York, N. Y., a corporation of Delaware Application July 3, 1948, Serial No. 36,841 7 Claims. (Cl. 178-61) This invention relates to telegraph systems,

vand more particularly to systems for transmitting signals having certain characteristics, over a transmission channel designed for transmission of signals of different characteristics.

A principal object of the invention is to provide a novel arrangement and organization of apparatus for enabling a single intelligence channel, e. g., a radio channel, to be used to convey intelligence signals arising at a pair of separate channels each of which is adapted to transmit intelligence signals by means of two elements, e. g., mark and space telegraph condiditions i Another object is to provide a novel arrangement for enabling two separate 2-element signal channels, to be connected to a single 4-element transmitting channel, so that at any given instant a single element in said transmitting channel represents intelligence from both the 2-e1e- 'ment channels. A typical example of such a transmitting channel is a carrier frequency shift channel.

Another object is to provide a novel arrangementfor receiving a single intelligence signal element which arisesv in two separate 2-unit channels, e. g., mark and space units, and automatically reproducing, under control of said singie element, the original 2-element signal conditions in said two channels for the purpose of operating respective telegraph printers or the like.

Another object isto provide a novel method of transmitting intelligence from two separate mark and space telegraph channels over a frequency shift transmission channel, whereby at any given instant the frequency represents inf-- telligence from both said telegraph channels.

Another object is to provide a frequency shift of the mark andspace signals from a pair or telegraph channels, and the respective output frequencies and their control voltages.

Fig. 1 is a graph showing the synchronized transition characteristic between the two telegraph channels. Fig. 2 is a chart showing the relation between the four output shifted fre.-` quencies and the four space-mark combination or conditions in the two channels to a transmitting channel.

Fig. 3 is a schematic diagram, partly in block form, of a complete system according to the invention. i

Fig. 4 is a graph of a typical characteristic curve of the frequency discriminator shown in Fig. 3.

Fig. 5 is a chart showing the relations between` periods of time.

2 the received frequencies and the segregated mark and space signals and their respective control voltages.

Referring to Fig. l, there are represented the current conditions arising in two separate telegraph channels of the mark and space type. Merely for purposes of explanation, it will be assumed that the space condition is represented by zero current, and the mark conditi-cn is represented by current of a certain minimum amplitude. It will be understood however, that the invention is equally useful` where the mark andspace conditions are represented by current reversals. It is apparent that there will be only four possible combinations between the mark and space elements of the two channels. These cornbinations can be represented by the elements of a single 4-element channel as follo'wsr" z-Eiement channel #1 @Element Channel #2 E* Space Space f1, I1, etc. Mark d jfraaetc. a. a, etc. Mark do f4, I4, etc.

In accordance with the invention, it will be assumed that the signals from the two channels (Fig. l) are to operate respective telegraph printers I, 2 (Fig. 3) which operate on the -unit or Baudot code principle. It will also be assumed that the originating signals from the two channels are to be transmitted over a radio or carrier channel of the frequency shift kind. In accordance with one phase of the invention, each of the above listed four conditions of the coinbined pair of 2unit channels is represented foy one of four dilerent frequencies, f1, f2, .fz, f4, only one of which is transmitted at a time over the radio channel.

If the two originating channels are keyed at random, the keying speed of the combined channels will be variable,` because some of the combinations listed above `may exist for very short lf, however, the two channels employ the same code, e. g., the 5'unit printer code, and the two channels are synchronized so that the transitions between mark and space occur simultaneously in `both channels as illustrated in Fig. l, then the keying speed of the combined channels will be the same as that of either of the single channels. Preferably, therefore, although not necessarily, automatic tape transmission is employed, although any other known method of synchronization maybe employed.

4-Element Circuit impulse is delivered to the trallmillters 1 3to step the tapes ahead to the next character;

The signal output current-from distributor 3;

is applied across a resistor I3.; and the` signaloutput current from distributor I9 is :applied across-a.

resistor I4, both resistors being connected in series across a pair of frequency shift input control terminals I5, I6. The resistors I3, I4 are respectivelylr proportioned or adjustedso that for a given mark signal in each channel',V the voltage developed across resistor I4 is, for example, twice that developed across resistor I3. rIhus the abovelisted four possible combinations of mark and, space elements will result in four respective values of voltage. For example, if a, mark signal Vin channel #l is represented by iive volts. across resistor I3, a mark signal in channel #2 will be represented by l volts across resistor I4. Consequently the four possible combinations will be represented respectively by four voltages, namely 0, 5, and 15 volts at the terminals I5, I6. These four voltage conditions can be transmitted by any well-known means to a receiving point for selective segregation purposes.

These four voltages, for example, are applied to the linear input of any well-known kind of frequency shifter I1 which produces four distinct frequencies f1, f2, f3, f4, in accordance with the said four voltages. Fig. 2 shows in chart form, the relation between the original four conditions of the pair of Z-element channels and the output frequencies from the shifter I1'. Thus the pair of 2-element telegraph channelsy are combined into a single 4-element channel by the process of converting the mark elements of the two telegraph channels into a form of energy so that the energy representing one channel is twice the energy representing the other channel, and then combining these energies in series and using the combined energy to key the 4-element channel. The simplicity of this process results from the representation of the four combinations of the 2-element channels by the respective frequency of the single 4-element channel in the following sequence:

Preferably, although not necessarily, the signals from shifter I1 are transmitted over a dual diversity radio channel, the radio transmitter being schematically represented by the block I8, and the dual diversity receiver being represented by the block I9. The output of receiver I9 is applied to any well-known frequency discrimination system by means of which the frequencies f1, fz, fs, f4 are converted into corresponding D. C. voltagesas illustrated for example by the graph of Fig. 4. These voltages are applied across a center-tapped resistor 2|, so that there are produced across this resistor four pairs of oppositely polarized voltage values E3, E4, as indicated in columns 8, 9 (Fig. 5).

Associated with resistor-ZI-'are four grid-controlled tubes 22, 23, 24, 25. The terminal 26 of resistor 2I is connected in parallel to the control grids 21, 28, 29, of respective tubes 22, 23, 24, While the terminal 30 is connected only to the control grid 3I of tube 25. It will be understood that the particular voltage values above mentioned, are arbitrarily chosen merely; forA explanatory purposes and-arenot. necessarily the. optimum values that may be used.

The center tap 32 of resistor 2| is connected to a` point, 3 3`I in, av voltage divider resistor which is bridgedacross-the D. C. power supply represented by the 1,00 voltv battery 34. The point 33 is chosen, under' the above-mentioned voltage ranges, so thatzitis lO volts removed from the 100 volt terminal 35. The point 33 is connected to-cathode 36'; and point 35 is connected to cathodgey1-'.A Another point 38 on the voltageV divider which is .20 volts positive with respect to point 35, and therefore 1Q volts` ppsitivewith respect to. pointA 3,3, is. connected. to Cathpde. 3.9. The

point 33" is also connected. tof cathode 40,. The points 3.5` and 3.8are therefore chosen' s o as to represent. approximately 2/3 the maximum, value of E34-E4 so that the, -valves and E4 will fall equally distant on either s ide ofthe three points 33,35, 38.

The ca thodes 36, 31, 3.9; 43, are connected to the taps adjacent the negative end or' the D. C. power supply, while their respective plates 4I, 742 43, 44,` are connected through suitable'- series resistors 4,5, 46, 4,1', to the positive end of' the D, C. power supply 341. The plates 4I, 42, of tubes 22,

Y 23, are directly connected by conductors 43', 49,

to the control'grids 5I),V 5I, of :associated tubes 52, 53. Likewise, the plates 43, 44, are connected in parallel anddirectly by conductor 54^toj the control grid 5,5 of an associated tube Y56. Thus'when no signals are being received from the discriminator 20, the grid of tube 2,2 is at zero bias'with respect to its cathode; the gridgof tube 23-"is biased l0 volts positive with respect toits cathode; the grid of tube 24 is 10 volts negative with respect to its cathode; andthe grid of tube V25 is at zero biasv with respect to its cathode. ItV will also be observed `that the tube 25'V is controlled only by the E4 voltage. The cathodes 51, 53, 59, ofA tubes 52, 53, 56, are connected to the grounded positive terminal ef the power supply 34. However, the plate 60of tube 52 is supplied by a separate D. C. power supply 6I, and theplates-62, 63, are connected in parallel to another separate D. C. power supply 64.

Connected in the negative lead 65 of powersupply 6I is a resistor 66. Likewise, connected' in the negative lead 61 of power supply 64 is a resistor 68. Any well-known tone keyer 69 is connected across resistor 68, and a similar tone keyer 19 is connected across resistor 66'. The keyers are so arranged that a negative voltage across their respective resistors 66, 68, placethese-keyers on space, while a positive voltage places them on mark.

Consider. now, tube'22 whose-cathode'is connected tothe -.90.volt point 33, andwhose grid is driven by the voltage E3. When frequencies f1 or f2 are beingreceived, the gridV voltage at grid 21 falls at points 35 and 38, namely sufficiently negative tokeep tube 22 at plate current cutoff, representing-a space signal as. indicated in columns 1, 3 and ID (Fig. 5) for frequencies fi. f2. However, when frequency f3 or f4 is being received, the grid 21 is driven positive and plate current ows through tube 22 to represent a mark signal. This; is indicated in Fig. ein the .columns 8, 9, I0, adjacent the frequencies fa, f4. Preferably, the grid of each of the tubes 22,-25 has `a resistance 'll-14 in useries ,with. it,` to prevent excessive positive excursions ofthe grids. M i

Considering now thetube 52, itr willbe :seen that when tube 22 is at cut off (i. e. on space), there is no current drawn thru anode load resistor 115 and consequently lno `voltage-drop is developed thereacross` and no bias is applied to grid 53 and therefore tube 52 `is `platecurrent conductive. Likewise, when tube 22 iscondur tive, tube 52 is at out off.` In other wordstubes 22 and 52 are conductive in opposite iphase as indicated in columns I and I I (Fig. In la Similar manner, when` tube 52 is atcut olf there is no bias applied to keyer, and both keyer 1i! and printer 2 are on mark; On `the other hand when tube 22 is on space (i. e. at cut olif), tube 52 is -conductive anda bias isapplied through resistor 56 to drivethe keyer 10 and the `printer to space. By a comparison of columns l2 and 2, it will be seen that channe1'1#2 has been eiTectively separated soV `as to control only `the printer2. 1 i 1- u By the same process it `will be seen that tube 24 is onspace (i. e. Aat cut off) for frequencies f1, f2, f3, so long as E3 is atthe voltage of points 3l,` 35, 38, l Similarly tube 25, whose grid is fed by Eli, is on spacefor frequencies f3, f4, while E4 is at the voltage of 33 or 35. These values of mark and space are indicated in columns I3, I 4, of Fig. 5.

The platesof tubes 24; 25, being in parallel, it will be seen that should both be on space, then a mark condition `on 'grid of tube 3I will cause a current` to. ow through their common plate resistor -lll. Therefore, tube 56 will go to mark only when 'both tubes 24, 25, are on space. Like- Wise, when either tube 24 or 25, or Aboth tube 24 and 25, are on mark, tube 56 will be on space. rhis is indicated in columns, I5, I6 (Fig. 5) wherein column I5 shows amark condition when either tube or 25 is at mark.

Now considering tube 23, it will be seen from column I1 that it will be on space only for frequency f1, and it will be on mark only for frequencies f2, fr, f4. As a result, tube 53 will `be in opposite phase as indicated in column I8. The plates of tubes 53 and 55 being in parallel, operate in combination similarly to the pair of tubes 24, 25. In other words, Iboth tubes 53, 56, must 'be on space, in order to remove the bias across keyer 69 so as to drive it to mark. The combination of tubes 53, 56, is indicated in column I9 and the resultant condition of keyer 69 and printer I are indicated in column 20. It will be noted that the conditions in column 20 correspond to those of channel #l (column I, Fig. 2), and thus the 2element channel #l has been reformed and the signals arising in that channel are reproduced only on printer I. Instead of a printer, any other signal reproducing device responsive to a 2element code can be used.

Any of the well-known means may be employed to prevent false operation by reason of hits or drop outs affecting the radio link due to static or other interference and to fading. To minimize the printing of erroneous characters as a result of these effects, the radio circuit can be operated in the well-known manner on a 'l-unit code basis by inserting any wellknown 5 to 7 unit translators at the transmitting end as represented by the dotted rectangle 15, 16,- and corresponding 7 to 5 unit translators 11, 18, at the receiving end.

y While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this `What isclaimed is:

1. An electron switch arrangement for `converting four selectively received frequencies into separate mark and space signals for use in two separate channels, comprising a frequency discriminator circuit, a rst set of four grid-controlled tubes coupledto said circuit, each of said tubes differently biassed to be responsive to the output of said circuit, a second set of three gridcontrolled tubes, each of the tubes of said sets having a grid, a cathode and a plate, a rst signal reproducer `channel connected to the plate circuit of the rst tube in the second set, another signal reproducer channel connected in parallel to the platecircuit of the second and third tubes of the second set, the plates of the lirst and second tubes of said rst set each respectively connected to said first and second tubes of said second set to vary the grid bias thereof, the plates of said third and fourth tubes of said nrst setconnected to the third tube of said `second set to vary the grid bias thereof so that the receipt by said discriminator circuit of one frequencyv causes both reproducer channels to go tospace, a second frequency causes both reproducer channels to go to mark, a third frequency causes the first reproducer channel to go to mark and the second reproducer channel to go to space, and a fourth rst reproducer channel to second reproducer channel 2. A telegraph transmitter go to space and the to go to mark.

generate a carrier frequency and means to apply said control voltages to said channel, means to shift the carrier frequency to any one of four distinct frequencies each representing one of said four combinations.

3. A telegraph transmitter according to claim 2 in which each of said telegraph channels includes a multiplex tape controlled transmitter each having an output distributor, and a common motor for driving said distributors in synchromsm.

4. A telegraph transmitter according to claim 2 in which the means to combine said voltages comprises a pair of resistors each connected respectively across the output of a corresponding one of said telegraph channels, said resistors being connected in series and being mutually proportioned in value so that a mark signal from one channel produces twice the voltage across its respective resistor as is produced by a 'mark minals ofi said series". ccrirfectexin resistors and' Whose output.v controlsl the: carmen shift oli said radio; transmitter;

' 6*.. A- telegraph receivercomprsingirif combina; tion, a frequency: shim radio: receiver arranged to respondltoffourfdiflerentreceiver carrierfshift's to producevtwolsets-fof four diierentvoltafgesga set of four grid-controlled electron tubesJneans to apply the voltages of one setr'tofselectivellyicontrolv the"conductvityy of three.- of the'tubes Aof s'aid set of A four tubes, meansfto' apply-' the' vvoltages` of the other setto.' selectively' controlthe conclue'- tivity only of. the fourtlif tube of-rsaidfsetof-our tubes, another set ofthree gridPeoritrol-lecl"t'ubes, means connectingr thefplatei` of: the -r'sttub'e of said three tubes ci the frstfset-f te:v oneL signal reproducing channel means connecting thefpla'tes of the remaining-1 two tubes of the'Y otherffset'ln parallel to a second? sgnalmeproducing channel; means connecting the platesl of. the firstl and secondwtubesvof the first-*set respectively t'o the grids, of. the firstsand-second ftubes ofwthe ether set, andmeans connecting,theplatesfv of thefthird and fourth tubesofrtl'ie'rst settin parallektothe grid of the thrdtubeof thevot'her set.-

7. A system oftelegraph communication-.comprising combination a,,rado.-transmitter` of=-th`e frequency shift.' Kind;v .aJv pair= 01'1V telegraphetransmitters" ea'c'h arr'an'gecf` to. transmitf respective mark and.' spaceLsig'nals 1 from. a pair. ofi channels,y means' to synchronize the transition` between mark' and space conditions in said channels,- a first" voltage dvelopi'ngnetworkl for coupling the signalsfrQmsaid'chaels'to said'lradotransmitter toprodce'fo'ur dii'erent carrier frequency apply thei voltages of the: other? settorselectively controli ther conductivity' onlyr o'ff the. fourthl tbe of'l said. t'bebanli; ani additional'- bankf o'- tliree grid-controlledelectron@tubefmeas connecting the plate 4oftl-ieffr` 'tuke ofsai'd additional banks tof4 ai lfirst of f saidffs'ignalv` reproducersi. neans' c'onnectingthefplates-of theremaning t'vvo tubes of said additionalbankL Vinparallel-i to'f thee other of said signali reproducersy. means?- conneeting the plates of the rst and second tubes of the'rstmentioned bank. respectively 15o/ftheM grids' off the rstand-l second tubes` of saidv additonarl bank; andfrneans-y connect-ing thee platesh of the third andfur'th ti-ibesvoil said\rstbanlf-in parallel to the'gridvof -the third-tube eflsaidr-additional bank', whereby,- said-lifeproducers areautematically operd atedin .accordanee'withqsignals only' from a respectve one of said telegraph transmitters.

SAMUELD. BRQWNING; 

